Asymmetric measurement-based dynamic packet assignment system and method for wireless data services

ABSTRACT

A method and system for assigning downlink and uplink channels to a mobile station registered with a base station, which uses an interference-sensing scheme and which provides improved reliability and performance over conventional schemes. Pilot tones transmitted by active mobile stations registered with the base station are turned off, each corresponding to an assigned downlink channel. Pilot tones being transmitted by the base station are turned off, each corresponding to an uplink channel assigned to one of the active mobile stations. The mobile station is paged from the base station with a pending traffic packet and requests access for a traffic packet. Interference sensing is performed at the base station to identify interference-free downlink channels and at the active mobile stations to identify interference-free uplink channels. A list of uplink channels identified as being acceptably interference-free is transmitted from each of the active mobile stations. A downlink traffic channel is assigned at the base station to the mobile station to receive the pending packets. An uplink channel is assigned to the mobile station at the base station. The channel assignments are transmitted from the base station to the mobile station. The downlink channels and uplink channels may be assigned to a plurality of mobile stations registered with the base station. There may be a plurality of base stations and the method may be performed successively for each of the plurality of base stations.

[0001] Benefit is hereby claimed under 35 USC 119(e) of the U.S.Provisional Application filed Mar. 23, 2000 and assigned Ser. No.60/191,500.

FIELD OF THE INVENTION

[0002] The invention disclosed is related to measurement-based dynamicpacket assignment for wireless data services.

RELATED ART

[0003] This application is related to U.S. Pat. No. 5,404,574 to M.Benveniste, for “Apparatus and Method for Non-Regular Channel Assignmentin Wireless Communication Networks,” and to U.S. Pat. No. 5,809,423 for“Adaptive-Dynamic Channel Assignment Organization System and Method.”

BACKGROUND OF THE INVENTION

[0004] The increased popularity of personal mobile communication and ofportable computing will significantly increase the demand for wirelesscommunication capacity, since they are heavy users of e-mail andweb-browsing applications. Access through fixed wireless communicationwill also contribute to this demand growth. Voice calls will increasethe circuit-switched traffic loads that have dominated wirelesscommunication up until now. The emerging convergence of voice and datatraffic into a single flow of IP packets will generate anever-increasing packet-switched traffic load. Resource utilizationefficiency is key to preserving the dynamic multiplexing advantagesachievable from this convergence. Regardless of its origin, theincreased demand will require more efficient methods of utilizing the RFspectrum allocated for this purpose.

[0005] Digital multiple access techniques must be optimized in order tomeet the growing demand for wireless communication capacity. The concernhere is with digital “channelized” methods, such as the North Americantime division multiple access (TDMA)/frequency division multiple access(FDMA) system defined by the IS-136 digital cellular standard or theEuropean TDMA/FDMA system defined by the Groupe Speciale Mobile (GSM)digital cellular standard. A channel in a TDMA/FDMA system is atime-slot. The objective in maximizing traffic-carrying capacity is toassign a channel to the unit of traffic load in a way that maximizes thesystem's throughput without violating quality-of-service (QoS)requirements. This is true whether it is a circuit-switched call thathas exclusive use of the circuit or a packet-switched call that sharesthe circuit with other calls.

[0006] New algorithms must be devised the meet an array of differentquality-of-service (QoS) requirements that arise with packet-switchedtraffic from diverse applications. Though the QoS requirements candiffer between different traffic types, their common objective andenvironmental/engineering constraints permit the use of similar channelassignment concepts for both. This is because the assignment of channelsto a packet in a packet-switched network resembles the assignment of achannel to a call for its duration in a circuit-switched network. Tounderscore this similarity, the terms packet and call are usedinterchangeably herein.

[0007] The notion of applying circuit-switched channel assignmentconcepts to packet-switched traffic should be pursued with care as thereexist fundamental differences. An important consideration relates to theasymmetry of the assignment in the two communication directions, theuplink direction from the mobile to the base station and the downlinkdirection from the base station to the mobile. With circuit-switchedvoice traffic, the uplink and downlink channels are paired, and channelassignment can thus utilize information available on only one direction.With packet-switched traffic, uplink and downlink channels would betypically independently assigned. A reason is the imbalance of thetraffic loads in the two directions: there is more traffic on thedownlink than on the uplink for certain applications, such as webbrowsing. But, even if the loads were balanced, channel assignmentshould occur independently in the two directions because of thenon-coincidence of uplink and downlink packets, even when occurringduring the same session.

[0008] Uncoupling the channel assignment for the two communicationdirections affects the applicability of circuit-switched trafficalgorithms to packet-switched traffic. An important considerationrelates to channel assignment algorithms relying oninterference-sensing, known also as measurement-based algorithms. Theproblem to be addressed is how to perform asymmetric measurement-basedchannel assignment on a single direction.

[0009] Another consideration in packet-switched channel assignment isthe packet length. Short “calls” require that the time dedicated tochannel assignment be short in order to avoid capacity loss. To carryout channel assignment efficiently in a multi-cell environment, themultiple base stations must be synchronized. With packets of constantlength, or of a small-integer multiple of a fixed length, channelselection by different base stations will occur simultaneously. In thatcase the possibility of contention for the same channel becomes likely.

[0010] I. Measurement Based Dynamic Channel Assignment (DCA)

[0011] There are two general forms of flexible channel assignment:adaptive, dynamic, and their combination known as adaptive-dynamic. Seefor example “Channel Assignment Schemes for Cellular MobileTelecommunication Systems: A Comprehensive Survey”, I. Katzela and M.Naghshineh, IEEE Personal Communications, June 1996. Also see the abovereferenced U.S. Pat. No. 5,404,574 and U.S. Pat. No. 5,809,423. Adaptivechannel assignment (ACA) is a time-variable fixed channel assignment(FCA), whereby the set of channels allocated for use by a base stationis fixed over a time interval, typically longer than the call duration.Dynamic channel assignment (DCA) also involves allocated sets ofchannels, whose membership may vary in time. The difference between thetwo is that the channel sets in ACA do not overlap and, moreimportantly, all allocated channels can be used simultaneously withoutviolating the pre-specified quality-of-service target. With DCA, on theother hand, this requirement on the composition of channel sets is notobserved. In fact, a common DCA approach employs channel sets comprisingall the available channels. Consequently, before a channel is assignedto a call by DCA, a test is required to establish observance of the QoSrequirement. The channel-assignment admissibility (channel assignmentadmissibility (CAA) criteria employed in this test vary.

[0012] The channel assignment admissibility (CAA) criterion may relyeither on real-time channel utilization information shared acrossneighboring base stations and combined with knowledge of theinterference relationships between base stations, or on real-timeinterference sensing. Dynamic channel assignment (DCA) algorithmsemploying the latter criterion are referred to as measurement-basedalgorithms. Such algorithms are particularly attractive for distributedsystem architectures as they require no real-time information sharingbetween base stations on channel utilization.

[0013] A. Measurement-based Channel Assignment Admissibility (CAA)Criterion

[0014] A measurement-based channel assignment admissibility (CAA)criterion delivers the target quality of service only if the utilizedmeasurements can predict reliably whether the channel assignment underconsideration will violate the quality-of-service requirement. Many ofthe proposed measurement-based dynamic channel assignment (DCA)algorithms fail to do so. The IS 136 digital cellular system uses themobile stations to measure the signals from surrounding base stationsand report those measurements back to the serving base station. This isprimarily used for mobile assisted handoff so that the network candecide whether a handoff is required. For channel assignment in an IS136 digital cellular system, the quality-of-service requirement will notbe met when the serving base station selects a channel for an incomingvoice call by relying exclusively on measurements of the signal strengthon downlink channels. Such measurements for channel assignment arecalled Mobile-Assisted Channel Assignment (MACA) measurements.

[0015] This situation is shown in FIG. 1, which depicts an indoorcellular system and an outdoor cellular system, respectively. In FIG. 1,mobile station 101 (MS1) is registered on base station 102 (BS1) andmobile station 103 (MS2) is registered on base station 104 (BS2). InFIG. 2, mobile station 201 (MS1) is registered on base station 202 (BS1)and mobile station 203 (MS2) is registered on base station 204 (BS2).The indoor system employs omni-directional base stations (withfull-aperture transmitters and receivers) housed within a building whosewalls, or other obstructions, may attenuate the transmitted signal. Theoutdoor system employs base stations with directional transmitters andreceivers that limit the coverage angle. In both systems, mobiles haveomni-directional receivers and transmitters. The common feature in thetwo systems is that a downlink signal from BS2 102 or 202 is hardlyperceptible by mobile MS1 101 or 201 because of the location of the two.An obstruction attenuates the signal in the indoor system, and themobile lies outside the beamwidth of the directional antenna of basestation BS2 in the outdoor system.

[0016] Suppose that Mobile MS2 103 or 203 is engaged in a call. Supposealso that a call is initiated by mobile MS1 101 or 201 and that the listof channels sent to mobile MS1 101 or 201 by base station B1 102 or 202for MACA measurement includes the channel used by mobile MS2. Because ofits location, the signal measured by mobile MS1 101 or 201 on thechannel used by mobile MS2 103 or 203 will be sufficiently weak to leadto the assignment of that channel to the incoming call. This assignmentwill cause interference to mobile MS2 103 or 203, and hence violate thequality-of-service requirement, because the CAA criterion used wasinadequate. In general, a CAA criterion that relies on mobilemeasurements alone to sense interference will be inadequate.

[0017] A measurement-based channel assignment admissibility (CAA)criterion would meet the QoS requirement if measurement of theinterference potential of a channel assignment is made on the exact samepath to be traversed by the signals resulting from the assignment. Ingeneral, two types of measurements are needed in order to clear achannel for assignment. A measurement clearing the path between themobile and the neighboring base stations, and another between theserving base station and the mobiles served by neighboring basestations. Clearance of channels can be accomplished differentlydepending on whether uplink and downlink channels are paired or not.

[0018] II. Coupled Uplink and Downlink Channel Assignment

[0019] Channel assignment in circuit-switched wireless networks occursin pre-defined pairs of uplink and downlink channels. Suchcircuit-switched wireless networks are typically used to carry voicetraffic. In such systems a measurement-based channel assignmentadmissibility (CAA) criterion could rely on a single signal strengthmeasurement for both channels of the pair. See for example “DistributedPacket Dynamic Resource Allocation (DRA) for Wireless Networks”, J. F.Whitehead, Proc. of VTC '96, pp 111-115. That is, both the base stationand the mobile are engaged in measurement of the signal strength of acandidate pair of channels. The mobile's measurement clears the downlinkchannel and its associated uplink channel along all paths between themobile and the neighboring base stations. The base station's measurementclears the uplink channel and its associated downlink channel along thepath between the serving base station and the mobiles served byneighboring base stations.

[0020] It can be seen in FIGS. 1 and 2 that the coupled measurementswould provide the indication of the interference potential for thechannel pair. As explained earlier, a signal strength measurement bymobile MS1 101 or 201 alone indicates that there is no call on thedownlink channel used by mobile MS2 103 or 203 because the obstructionattenuates the signal in the indoor system, and the mobile lies outsidethe beam-width of the directional antenna of base station BS2. If, inaddition to mobile MS1 101 or 201 measuring the signal strength on thedownlink channel used in mobile MS2's 103 or 203 call, base station BS1102 or 202 also measured the signal strength on the paired uplinkchannel, there would be the indication that the pair of channels wasused by a neighboring base station and hence the assignment would not bemade.

[0021] III. Directionally-uncoupled Channel Assignment

[0022] Unlike in circuit-switched wireless systems, channel assignmentin packet-switched wireless systems requires uncoupling along the uplinkand downlink communication directions, as the traffic in the twodirections is non-coincident. That is, packets from the mobile and thebase station occur at different times. Thus uncoupling would be requiredeven if the traffic loads in the two directions were reasonablybalanced.

[0023] In theory, both frequency-division and time-division duplex cansupport uncoupled channel assignment between uplink and downlink.Time-division duplex allows more efficient channel training, andallocation of the radio resource between the two directions requires noplanning. With frequency-division duplex, a different number of channelswould be made available in the two directions when the traffic loadsalong the two directions differ. Additionally, the duration of themeasurement and channel selection must be short for, if it issignificant relative to the duration of a call, it would cause capacityloss.

[0024] The problem of accommodating unbalanced packet traffic loads byapplying a measurement-based channel assignment algorithm on a singledirection has been addressed in “An OFDM-Based High-Speed-Data (HSD) AirInterface Proposal”, J. C. Juang and S. Timuri, AWS submission to theUniversal Wireless Communications Consortium UWCC GTF HSD/97.10.0709,Nov. 11, 1997. See also “Dynamic Packet Assignment for Advanced InternetCellular Services”, J. C. Chuang and N. R. Sollenberger, Proc. OfGlobecom '97. See also “Advanced Cellular Internet Service (ACIS)”, L.J. Cimini, Jr., J. C. Chuang, and N. R. Sollenberger, IEEECommunications Magazine, October 1998. A time division multiple access(TDMA)/frequency division multiple access (FDMA) frame structure wasproposed for downlink packet assignment, which was based on theOrthogonal Frequency Division Multiplexing (OFDM) technique formulti-carrier modulation. Pilot tones that correspond to the downlinktraffic channels in use are transmitted simultaneously by the basestations, thus enabling the mobiles to scan the pilots and completechannel assignment quickly. Mobiles with pending packets measure thetones transmitted by the neighboring base stations and report the listof interference-free channels to their serving base stations. Theserving base station then notifies the mobiles of the channel assignedto transmit the traffic packet. By staggering the time of channelselection, the possibility of contention for the same channel bydifferent base stations is avoided, which would be caused by theconcurrency of channel assignment among base stations. Interfering basestations do not engage in channel assignment at the same time.

[0025] While the above-described scheme satisfactorily addresses theissue of measurement delay and contention, it does not always lead tointerference-free channel assignments. Interference can result becausethe path traversed by the signal from the serving base station to themobiles served by neighbor base stations, is not the same as the pathtraversed by the signal transmitted by a neighbor base station andsensed by the mobile during the interference measurement. As illustratedin FIGS. 1 and 2, there could be instances whereby mobile MS1 101 or 201which is served by base station BS1, does not receive the pilot tonesfrom a neighboring base station, base station BS2, even though the pilotis transmitted. This could be due to an obstruction, or simply to theorientation of a directional antenna. Hence, if base station BS1 selectsthe channel corresponding to the missed pilot tone, it could causeinterference to mobile MS2 103 or 203, which is served by base stationBS2.

[0026] Thus, a need arises for an interference-sensing scheme for use inasymmetric channel assignment which provides improved reliability andperformance over conventional schemes.

SUMMARY OF THE INVENTION

[0027] The present invention is a method and system for assigningdownlink and uplink channels to a mobile station registered with a basestation. The present invention uses an interference-sensing scheme foruse in asymmetric channel assignment which provides improved reliabilityand performance over conventional schemes.

[0028] One embodiment of the present invention is a method of assigninga downlink channel to a mobile station registered with a base station.Pilot tones being transmitted by a plurality of active mobile stationsregistered with the base station are turned off. Each turned off pilottone corresponds to an assigned downlink channel. The mobile station ispaged from the base station with a pending traffic packet. Interferencesensing is performed at the base station to identify interference-freedownlink channels. A downlink traffic channel is assigned at the basestation to the mobile station to receive the pending packets and thedownlink channel assignment is transmitted from the base station to themobile station. The downlink channels may be assigned to a plurality ofmobile stations registered with the base station. There may be aplurality of base stations and the method may be performed successivelyfor each of the plurality of base stations.

[0029] Another embodiment of the present invention is a method ofassigning an uplink channel to a mobile station registered with a basestation. Pilot tones being transmitted by the base station are turnedoff. Each turned off pilot tones corresponds to an uplink channelassigned to one of a plurality of active mobile stations registered withthe base station. The mobile station requests access for a trafficpacket. Interference sensing is performed at the plurality of activemobile stations to identify interference-free uplink channels. A list ofuplink channels identified as being acceptably interference-free istransmitted from each one of the plurality of active mobile stations. Anuplink channel is assigned to the mobile station by the base station andthe uplink channel assignment is transmitted from the base station tothe mobile station. The uplink channels may be assigned to a pluralityof mobile stations registered with the base station. There may be aplurality of base stations and the method may be performed successivelyfor each of the plurality of base stations.

[0030] Another embodiment of the present invention is a method ofassigning an uplink channel and a downlink channel to a mobile stationregistered with a base station. Pilot tones being transmitted by aplurality of active mobile stations registered with the base station areturned off. Each turned off pilot tone corresponds to an assigneddownlink channel. Pilot tones being transmitted by the base station areturned off. Each turned off pilot tones corresponds to an uplink channelassigned to one of a plurality of active mobile stations registered withthe base station. The mobile station is paged from the base station witha pending traffic packet. The mobile station requests access for atraffic packet. Interference sensing is performed at the base station toidentify interference-free downlink channels. Interference sensing isperformed at the plurality of active mobile stations to identifyinterference-free uplink channels. A list of uplink channels identifiedas being acceptably interference-free is transmitted from each one ofthe plurality of active mobile stations. A downlink traffic channel isassigned at the base station to the mobile station to receive thepending packets. An uplink channel is assigned to the mobile station atthe base station. The downlink channel assignment and the uplink channelare transmitted from the base station to the mobile station. Thedownlink channels and uplink channels may be assigned to a plurality ofmobile stations registered with the base station. There may be aplurality of base stations and the method may be performed successivelyfor each of the plurality of base stations.

[0031] The resulting invention provides a reliable measurement-basedchannel assignment admissibility (CAA) system and method which isapplicable to unidirectional uplink or downlink channel assignment.

DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be more fully appreciated by referringto the accompanying drawings.

[0033]FIG. 1 is a depiction of a prior-art indoor cellular system.

[0034]FIG. 2 is a depiction of a prior-art outdoor cellular system.

[0035]FIG. 3 is an exemplary block diagram of a wirelesstelecommunications system, in which the present invention may beimplemented.

[0036]FIG. 4 is a flow diagram of a process of operation of the presentinvention.

[0037]FIG. 5 is a flow diagram of a downlink channel assignment process,according to the present invention.

[0038]FIG. 6 is an exemplary format of a superframe, in which theprocess shown in FIG. 5 is carried out.

[0039]FIG. 7 is a flow diagram of an uplink channel assignment process,according to the present invention.

[0040]FIG. 8 is an exemplary format of a superframe, in which theprocess shown in FIG. 7 is carried out.

[0041]FIG. 9 is a flow diagram of a downlink channel and uplink channelassignment process, according to the present invention.

[0042]FIG. 10 is an exemplary format of a superframe, in which theprocess shown in FIG. 9 is carried out.

[0043]FIG. 11 illustrates a frame structure for directionally uncoupledchannel assignment, in accordance with the invention.

[0044]FIG. 12 illustrates a hexagonal base station layout.

[0045]FIG. 13 illustrates a cloverleaf base station layout.

[0046]FIG. 14 is an example of a wireless telecommunications system,according to the present invention.

DISCUSSION OF THE PREFERRED EMBODIMENTS

[0047] An exemplary wireless telecommunications system 300, in which thepresent invention may be implemented, is shown in FIG. 3. System 300includes a plurality of wireless base stations, such as base stations302A through 302N. Each base station serves, or has registered with it,a plurality of mobile stations. For example, base station 302A hasregistered with it mobile stations 304A-1 through 304A-N, base station302B has registered with it mobile stations 304B-1 through 304B-N, andbase station 302N has registered with it mobile stations 304N-1 through304N-N. Each base station communicates with the mobile stationsregistered with that base station over wireless links. For example, basestation 302A communicates with mobile station 304A-1 over wireless links306 and 308 and with mobile station 304N over wireless links 310 and312. Links 306 and 312, which communicate from the mobile stations304A-1 and 304A-N, respectively, to base station 302A are termeduplinks. Links 308 and 310, which communicate from base station 302A tothe mobile stations 304A-1 and 304A-N, respectively, are termeddownlinks. Calls and/or packets, which terms will be usedinterchangeably hereinafter, are transmitted from the mobile station tothe base station over the uplink, while calls and/or packets aretransmitted from the base station to the mobile station over thedownlink.

[0048] A. Requirements of a Measurement-based Channel AssignmentAdmissibility (CAA) Criterion

[0049] If interfering base stations are engaged in channel assignmentconcurrently, it is possible that they would select the same channel.Staggering the time when measurement and channel selection decisions aremade by interfering base stations, would avoid contention. A reliablechannel assignment admissibility (CAA) criterion is obtained foruncoupled channel assignment by returning to the basic requirement: thatall the paths along which the assigned channel will traverse must becleared.

[0050] 1. Downlink Communication Direction

[0051] Considering downlink channel assignment first, the channelassignment admissibility (CAA) criterion would require that

[0052] (i) the signal transmitted on the candidate downlink channel bereceived by the mobile without interference, and

[0053] (ii) the channel assignment cause no interference to activeneighboring mobiles.

[0054] To satisfy the first point, the mobile with a pending packet mustclear the candidate downlink channels by measuring the received signalstrength and communicate this information to the serving base station.If the signal is weak, the first criterion will be met. In order toestablish the requirement (i) for the downlink CAA criterion one coulduse a feature like MACA (mobile assisted channel assignment) availablein the IS 136 and the GSM air interface standard. Paged mobiles (mobileswith packets pending) would scan candidate downlink channels and measurethe received signal strength. Alternatively, when channel reservationand data transmission are separated, the base station could transmitsimultaneously pilot tones that correspond to its assigned downlinktraffic channels F. Furuya and Y. Akaiwa, “Channel segregation, adistributed adaptive channel allocation scheme for mobile communicationssystems”, Trans. IEICE, Vol. E74, June 1991, pp. 1531-1537. Page mobilesscan the transmitted pilots to identify the acceptable downlinkchannels, of which they would inform their base station. A list, ratherthan the best channel, is returned to the serving base station, in casemore than one mobile report the same channel and in order to accommodatedifferent bit rates through time-slot pooling.

[0055] In order to meet criterion (ii), it is necessary to establishwhether an active mobile that can be reached at sufficient intensity bya signal emanating from the serving base station, uses the candidatechannel. In accordance with the invention, the following two equivalentconditions are established:

[0056] (ii.1) whether there are any active mobiles that can be reachedby a signal from the serving base station; and

[0057] (ii.2) whether any of the mobiles so identified use the candidatedownlink channel.

[0058] The first question can be answered by having the serving basestation engage in a measurement of a signal transmitted by the activemobiles on the uplink control channel. By the symmetry found inpoint-to-point connections, a strong uplink received signal wouldindicate that the signal on the reverse path would be also strong. Thesecond question can be answered by requiring the control signal toindicate the identity of the downlink channel used by the mobile. Forinstance, the active mobiles (mobiles with pending packets that havealready been assigned a channel) transmit on the uplink control channelpilot tones that correspond to their assigned downlink channel. Theserving base station scans the pilots to obtain a measure of both theproximity and, hence, the interference potential from (and to) nearbyactive mobiles and of the downlink channels these mobiles use. The basestation assigns a downlink channel by eliminating from the list ofacceptable channels received from the paged mobile the downlink channelsalready assigned to nearby active mobiles.

[0059] 2. Uplink Communication Direction

[0060] The channel assignment admissibility (CAA) criterion for uplinkchannel assignment is expressed similarly as the requirement that

[0061] (i) the signal transmitted on the candidate uplink channel bereceived by the base station without interference, and

[0062] (ii) the channel assignment cause no interference to neighboringbase stations.

[0063] To answer the first question, it is sufficient for the servingbase station to clear the candidate uplink channels by measuring thereceived signal. If the signal is weak, the first criterion will be met.The serving base station scans the uplink traffic channels and measuresinterference. This could be readily achieved with existing systems byadding a radio at the base station cite. Alternatively, narrow bandtones corresponding to the uplink channels used by active mobiles aretransmitted by all such mobiles and scanned by the serving base station.A list of acceptable uplink channels is thus constructed.

[0064] In order to meet criterion (ii), it is necessary to establishwhether a base station that can be reached at sufficient intensity by asignal from the mobile with a pending packet uses the candidate uplinkchannel. In accordance with the invention, the following two equivalentconditions are established:

[0065] (ii.1) which base stations can be reached by a signal from themobile with the channel request; and

[0066] (ii.2) whether any of the base stations so identified use thecandidate uplink channel.

[0067] The first question can be answered by having the paged mobilemeasure the signal transmitted on the downlink control channel by theneighboring base stations. As before, because of the symmetry inpoint-to-point connections, a strong downlink received signal wouldindicate that the signal on the reverse path would be also strong. Thesecond question can be answered by requiring each base station toindicate on its control the identity of the uplink channels used by themobiles served by that base station. For instance, the base stationtransmits on a downlink control channel pilot tones that correspond totheir assigned uplink channels. A paged mobile scans the pilots toobtain a measure of both its proximity and, hence, the interferencepotential from (and to) neighboring base stations and of the uplinkchannels nearby base stations use. The list of noisy uplink channels isconveyed to the serving base station. The base station assigns an uplinkchannel by eliminating from the list of acceptable channels the list ofnoisy channels received from the paged mobile.

[0068] The interference-sensing scheme of the present inventionidentifies channel use by neighboring cells reliably. A process ofoperation of the present invention is shown in FIG. 4. The processbegins with step 402, in which all active mobile stations transmit pilottones on the uplink. Each active mobile station transmits a tonecorresponding to the downlink channel it has been assigned. In step 404,the base stations monitor the pilot tones transmitted by the mobilestations. In step 406, the mobile stations covered by a given basestation will turn off their pilot tones in the assignment frame, whichoccurs on a staggered schedule for each base station. This allows eachbase station to determine the cell location of each mobile station whosepilot tone the base station is receiving, and thus determine the channelusage of mobile stations in neighboring cells. In step 408, using theinformation relating to channel usage of mobile stations in neighboringcells, each base station selects interference-free channels for itsmobile stations. In step 410, each base station transmits the channelassignments to each of its mobile stations.

[0069] B. Implementation of Proposed Interference-sensing Scheme

[0070] The above schemes can be implemented with a variety ofcontrol/signaling mechanisms. The implementation method would depend onthe type of traffic, that is, the length of the packet or call and theduration of the measurement and channel selection relative to the packetlength. Shorter packets would require faster measurement and channelselection mechanisms. A description of the inventive method is presentedfor short packet traffic.

[0071] 1. Downlink Channel Assignment

[0072] In order to establish condition (i) for the downlink channelassignment admissibility (CAA) criterion one can use a feature likemobile assisted channel assignment (MACA) available in the IS 136 andthe GSM air interface standard. Paged mobiles (mobiles with packetspending) scan candidate downlink channels and measure the receivedsignal strength. Alternatively, in order to reduce measurement delay,the base station could transmit simultaneously pilot tones thatcorrespond to its active downlink traffic channels. See the L. J.Cimini, Jr., et al. reference cited above. Paged mobiles scan thetransmitted pilots to identify the acceptable downlink channels, ofwhich they would inform their base station. A list, rather than the bestchannel, is returned to the serving base station, in case more than onemobile report the same channel and in order to accommodate different bitrates through time-slot pooling.

[0073] Criterion (ii) can be established by requiring the active mobiles(mobiles with pending packets that have already been assigned a channel)to transmit on an uplink control channel pilot tones that correspond totheir assigned downlink channel. The serving base station scans thepilots to obtain a measure of both the proximity and, hence, theinterference potential from (and to) nearby active mobiles and of thedownlink channels these mobiles use. The base station assigns a downlinkchannel by eliminating from the list of acceptable channels receivedfrom the paged mobile the downlink channels already assigned to nearbyactive mobiles.

[0074] A process of channel assignment, according to the presentinvention, which is applicable to assign downlink channels for one-waytraffic from the base station to one or more mobile stations, is shownin FIG. 5. The process begins with step 502, in which the active mobilestations registered with the base station turn off the pilot tonescorresponding to their assigned downlink channels. In step 504, the basestation pages the registered mobiles with pending traffic packets. Instep 506, the base station performs interference sensing to identifyinterference-free downlink channels. In step 508, the base stationassigns downlink traffic channels to the paged mobiles to receive theirpending packets. In step 510, the base station transmits the channelassignments to the mobile stations. In all other frames of a superframethe active mobiles registered with the base station will transmit theirpilot tones corresponding to the assigned downlink channels.

[0075] Each base station is assigned a frame within each superframe, inwhich the process shown in FIG. 5 is carried out. Since the mobilesserved by interfering base stations turn off their pilots in thedifferent frames within a superframe, the number of frames persuperframe must be equal to at least the re-use factor needed to deliverthe desired reception. An exemplary frame structure, according to thepresent invention, is shown in FIG. 6. The depicted frame structureassumes that there is one-way traffic from the base station to themobile. Frame structure 600 is an example of a downlink frame structure,while frame structure 602 is an example of an uplink frame structure.

[0076] Downlink frame structure 600 includes a plurality of superframes,such as super-frames 604A to 604Z. Each superframe includes a pluralityof assignment frames, such as assignment frame 606, which is theassignment frame for an exemplary base station, designated BS1. Eachassignment frame is used to determine channel assignments for eachneighboring base station. Each assignment frame includes a plurality ofsegments, such as segments 607 and 608, in which transmissions from thebase station to one or more mobile stations occur. For example, insegment 607, base station BS1 pages the active mobile stationsregistered with base station BS1, as in step 504 of FIG. 5. In segment608, base station BS1 transmits the selected downlink channels to themobile stations, as in step 510 of FIG. 5.

[0077] Uplink frame structure 602 includes a plurality of superframes,such as super-frames 610A to 610Z. Each superframe includes a pluralityof assignment frames, such as assignment frame 612, which is theassignment frame for an exemplary base station, designated BS1. Eachassignment frame is used to determine channel assignments for eachneighboring base station. Each assignment frame includes a plurality ofsegments, such as segment 614, in which transmissions from one or moremobile stations to the base station occur. For example, in segment 614,the mobile stations registered with base station BS1 stop transmittingtheir pilot tones, as in step 502 of FIG. 5, and the mobile stations ofbase stations other than base station BS1 transmit their pilot tones.

[0078] 2. Uplink Channel Assignment

[0079] Uplink channel assignment is similar to downlink channelassignment. Condition (i) for the uplink channel assignmentadmissibility (CAA) criterion would require the serving base station toscan the uplink traffic channels and measure interference. This could bereadily achieved with existing systems by adding a radio at the basestation cite. Alternatively, narrow band tones corresponding to theuplink channels used by active mobiles are transmitted by all suchmobiles and scanned by the serving base station. A list of acceptableuplink channels is thus constructed.

[0080] Criterion (ii) can be established by requiring the base stationsto transmit on a downlink control channel pilot tones that correspond totheir assigned uplink channels. A paged mobile scans the pilots toobtain a measure of both its proximity and, hence, the interferencepotential from (and to) neighboring base stations and of the uplinkchannels nearby base stations use. The list of noisy uplink channels isconveyed to the serving base station. The base station assigns an uplinkchannel by eliminating from the list of acceptable channels the list ofnoisy channels that was received from the paged mobile.

[0081] In general, when one-way traffic from the mobile to the basestations is involved, the roles of the base stations and mobiles arereversed. A process of channel assignment, according to the presentinvention, which is applicable to assign uplink channels for one-waytraffic from one or more mobile stations to the base station, is shownin FIG. 7. The process begins with step 702, in which the base stationturns off its pilot tones corresponding to the assigned uplink channels.In step 704, the mobile stations registered with base station BS1, whichare generating traffic packets, request access for those packets. Instep 706, the active mobile stations engage in interference sensing toidentify interference-free uplink channels. In step 708, each activemobile station transmits to the base station its list of uplink channelsthat it identified as being acceptably interference-free uplinkchannels. In step 710, the base station examines the received lists ofchannels, selects channels that are overall acceptablyinterference-free, and assigns uplink channels to the mobile stationsthat requested access in step 704. In step 712, the base stationtransmits the channel assignments to the mobile stations that requestedaccess. In all other frames of a superframe the base station willtransmit its pilot tones corresponding to the assigned uplink channels.As described above, since the interfering base stations do not turn offtheir pilot tones in the same frame, the number of frames per superframemust be at least equal to the re-use factor needed to deliver thedesired reception quality.

[0082] Each base station is assigned a frame within each superframe, inwhich the process shown in FIG. 7 is carried out. An exemplary framestructure, according to the present invention, is shown in FIG. 8. Thedepicted frame structure assumes that there is one-way traffic from amobile station to the base stations. Frame structure 800 is an exampleof a downlink frame structure, while frame structure 802 is an exampleof an uplink frame structure.

[0083] Downlink frame structure 800 includes a plurality of superframes,such as super-frames 804A to 804Z. Each superframe includes a pluralityof assignment frames, such as assignment frame 806, which is theassignment frame for an exemplary base station, designated BS1. Eachassignment frame is used to determine channel assignments for eachneighboring base station. Each assignment frame includes a plurality ofsegments, such as segments 807 and 808, in which transmissions from basestations to one or more mobile stations occur. For example, in segment807, base station BS1 turns off its pilot tones corresponding to theassigned uplink channels, while base stations other than BS1 continue totransmit their pilot tones, as in step 702 of FIG. 7. In segment 808,base station BS1 transmits the assigned uplink channels to the mobilestations, as in step 712 of FIG. 7.

[0084] Uplink frame structure 802 includes a plurality of superframes,such as super-frames 810A to 810Z. Each superframe includes a pluralityof assignment frames, such as assignment frame 812, which is theassignment frame for an exemplary base station, designated BS1. Eachassignment frame is used to determine channel assignments for eachneighboring base station. Each assignment frame includes a plurality ofsegments, such as segments 814 and 816, in which transmissions from oneor more mobile stations to the base station occur. For example, insegment 814, the mobile stations registered with base station BS1, whichare generating traffic packets, request access for those packets, as instep 704 of FIG. 7. In segment 816, each active mobile station transmitsto the base station its list of uplink channels that it identified asbeing acceptably interference-free uplink channels, as in step 708 ofFIG. 7.

[0085] II. Medium Access Control for Packet Traffic

[0086] In accordance with the invention, a scheme for uncoupling thechannel assignment of uplink and downlink traffic is presented.Additional considerations are posed by packet traffic, namely the needfor fast channel assignment decisions and the avoidance of contention.Certain concepts can be borrowed from the interference-sensing schemeproposed for downlink channel assignment in the L. J. Cimini, Jr., etal. reference cited above, as it addresses some of these issuessatisfactorily. The invention differs from that scheme by eliminatingthe interference that would occur occasionally due to insufficientmeasurement data, the introduction of some equity features, and QoSawareness. Additionally, in accordance with the invention, aninterference-sensing scheme for uplink channel assignment is provided.

[0087] A. The Method

[0088] In accordance with the invention, a medium access control schemeis provided for uncoupled downlink and uplink channel assignment thataccommodates packet of fixed length (as with ATM) or variable length (aswith IP). the invention works with either frequency-division andtime-division multiplex techniques.

[0089] In accordance with the invention, narrow-band pilot tones areused, corresponding to assigned traffic channels, as seen in the L. J.Cimini, Jr., et al. reference cited above. Such tones can be scannedquickly and conveniently with OFDM modulation. While using strongsynchronization between base stations and their mobiles, scanning of thepilot tones is staggered in order to avoid contention for the samechannel between mutually interfering base stations with concurrenttraffic. A base station is assigned within each super-frame a frame,referred to as the assignment frame, during which it transmits itstones. Mobiles scan the tones and report a list of channels with lowinterference to the serving base station. The base station selects achannel and notifies the mobile.

[0090] The interference-sensing scheme in the L. J. Cimini, Jr., et al.reference cited above, is modified as follows. First, in addition torequiring the base stations to transmit tones corresponding to thedownlink channels acquired for their use, the active mobiles also do thesame on the uplink. That is, all active mobiles transmit a tonecorresponding to the downlink channel each mobile has been assigned.And, in addition to the mobiles engaging in signal measurement (andtransmission of the list of admissible channels to the base station),the serving base station will also listen to the tones transmitted bythe active mobiles. In order to be able to stagger channel-assignmenttimes, the active mobiles will turn off their pilots during their basestation's assignment frame, just like the base station will turn off itspilot tones during its channel assignment frame so that mutuallyinterfering base stations do not select channels concurrently. From itsmeasurements, the base station thus constructs its own list ofadmissible channels. Eliminating the channels absent from the basestation's list of admissible channels will shorten the list ofadmissible channels received from the paged mobile.

[0091] An analogous interference-sensing scheme is proposed for uplinkchannel assignment. Instead of transmitting tones that correspond toassigned downlink channels, all the base stations and their activemobiles transmit tones corresponding to the assigned uplink channels.

[0092] In theory, both frequency-division and time-division duplex cansupport uncoupled channel assignment between uplink and downlink. Withfrequency-division duplex, a different number of channels would be madeavailable in the two directions when the traffic loads along the twodirections differ.

[0093] A process of channel assignment, according to the presentinvention, which is applicable to assign uplink channels for asymmetrictwo-way traffic between one or more mobile stations and the basestation, is shown in FIG. 9. The process begins with step 902, theactive mobile stations registered with the base station turn off thepilot tones corresponding to their assigned downlink channels, whileactive mobile stations registered with base stations other than thatbase station continue transmitting their pilot tones. In step 904, thebase station turns off its pilot tones corresponding to the assigneduplink channels. In step 906, the base station pages the registeredmobiles with pending traffic packets. In step 908, the mobile stationsregistered with base station BS1, which are generating traffic packets,request access for those packets. In step 910, the base station performsinterference sensing to identify interference-free downlink channels. Instep 912, the active mobile stations engage in interference sensing toidentify interference-free uplink channels. In step 914, each activemobile station transmits to the base station its list of uplink channelsthat it identified as being acceptably interference-free uplinkchannels. In step 916, the base station assigns downlink trafficchannels to the paged mobiles to receive their pending packets. In step918, the base station examines the received lists of channels, selectschannels that are overall acceptably interference-free, and assignsuplink channels to the mobile stations that requested access in step904. In step 920, the base station transmits the channel assignments tothe mobile stations that requested access. In all other frames of asuperframe the active mobile stations registered with the base stationwill transmit their pilot tones corresponding to the assigned downlinkchannels and the base station will transmit its pilot tonescorresponding to the assigned uplink channels. As described above, sincethe interfering base stations do not turn off their pilot tones in thesame frame, the number of frames per superframe must be at least equalto the re-use factor needed to deliver the desired reception quality.

[0094] Each base station is assigned a frame within each superframe, inwhich the process shown in FIG. 9 is carried out. An exemplary framestructure, according to the present invention, is shown in FIG. 10. Thedepicted frame structure assumes that there is two-way traffic from amobile station to the base stations. Frame structure 1000 is an exampleof a downlink frame structure, while frame structure 1002 is an exampleof an uplink frame structure.

[0095] Downlink frame structure 1000 includes a plurality ofsuperframes, such as super-frames 1004A to 1004Z. Each superframeincludes a plurality of assignment frames, such as assignment frame1006, which is the assignment frame for an exemplary base station,designated BS1. Each assignment frame is used to determine channelassignments for each neighboring base station. Each assignment frameincludes a plurality of segments, such as segments 1006, 1007, 1008, and1009, in which transmissions from base stations to one or more mobilestations occur. For example, in segment 1006, base station BS1 pages theactive mobile stations registered with base station BS1, as in step 906of FIG. 9. In segment 1007, base station BS1 turns off its pilot tonescorresponding to the assigned uplink channels, while base stations otherthan BS1 continue to transmit their pilot tones, as in step 904 of FIG.9. In segment 1008, base station BS1 transmits the assigned uplinkchannels to the mobile stations, as in step 920 of FIG. 9. In segment1009, base station BS1 transmits the assigned downlink channels to themobile stations, as in step 920 of FIG. 9.

[0096] Uplink frame structure 1002 includes a plurality of superframes,such as super-frames 1010A to 1010Z. Each superframe includes aplurality of assignment frames, such as assignment frame 1012, which isthe assignment frame for an exemplary base station, designated BS1. Eachassignment frame is used to determine channel assignments for eachneighboring base station. Each assignment frame includes a plurality ofsegments, such as segments 1014, 1016, and 1018, in which transmissionsfrom one or more mobile stations to the base station occur. For example,in segment 1014, the mobile stations registered with base station BS1,which are generating traffic packets, request access for those packets,as in step 908 of FIG. 9. In segment 1016, the active mobile stationsregistered with the base station turn off the pilot tones correspondingto their assigned downlink channels, while active mobile stationsregistered with base stations other than that base station continuetransmitting their pilot tones, as in step 902 of FIG. 9. In segment1018, each active mobile station transmits to the base station its listof uplink channels that it identified as being acceptablyinterference-free uplink channels, as in step 914 of FIG. 9.

[0097] B. The Time-division Duplex Method

[0098] A frame structure description for uncoupled channel assignment ispresented in the context of a time-division duplex arrangement. Eitherdownlink or uplink channels can be assigned by the proposed scheme,which can also accommodate the uncoupled channel assignment on the twodirections concurrently. The proposed scheme is described in the contextof the latter. Time-division duplex allows the allocation of the radioresource between the two directions without the need for planning.Moreover, it can achieve more efficient channel training.

[0099] The concepts presented here can be used with protocols for fixedlength packets (like ATM packets) or for variable-length packets (likeIP packets). If the traffic involves variable-length packets, which aremultiple time-slots in length, several channels (time slots) may bereserved within the same super-frame in order to achieve higher user bitrates. It is also possible to achieve continuous transmission of apacket over several super-frames without the need for channelreselection. The extent to which these options are exercised will dependon the QoS priority of the packet stream, inter-stream synchronization,and other traffic management considerations. As these options are thepurview of the particular channel assignment algorithm employed, theirimplementation is left out of this discussion.

[0100] Each super-frame comprises a set of assignment frames to be usedfor channel assignment/reservation purposes, plus additional segments tobe used for reserved and unreserved traffic, in either direction. Eachbase station is scheduled to perform channel assignment during one ofthe assignment frames. In subsequent assignment frames, the base stationhelps coordinate the channel assignment process of its neighbor basestations. Specifically, in frames following its scheduled assignmentframe, a base station will transit pilot tones corresponding to thechannels that have already been reserved for its use for thatsuperframe. The reserved channels could be either uplink channels ordownlink, or both if a base station is handling both types on traffic ina super-frame. The pilot tones of the reserved channels will continue tobe transmitted over all super-frames for which a channel has beenreserved. In all assignment frames other than the scheduled assignmentframe, the active mobiles of a base station (which are the mobiles thathave already been paged and undergone channel assignment for the presentsuper-frame) will transmit tones corresponding to the channel(s)reserved for their respective use.

[0101] As illustrated in FIG. 11, the assignment portion of thesuper-frame consists of alternating downlink and uplink segments, whichare separated by an idle time interval to allow the radios to switchfrom transmitting to receiving. An assignment frame comprises a downlinkpaging sub-frame, a downlink measurement sub-frame, followed by anuplink measurement sub-frame, and an uplink reporting sub-frame, thenfollowed by a downlink notification sub-frame.

[0102] During the assignment frame of a base station, the followingcontrol functions will be carried out:

[0103] the base station turns off its pilots;

[0104] the active mobiles served by the base station turn off theirpilot tones;

[0105] the base station pages its registered mobiles with pendingtraffic packets on the downlink paging sub-frame;

[0106] the paged mobiles are engaged in interference sensing on thedownlink measurement sub-frame to identify interference-free channels;

[0107] the base station engages in interference sensing on the uplinkmeasurement sub-frame to identify interference-free channels;

[0108] the list of acceptable channels are reported by the paged mobilesto the base station on the uplink reporting sub-frame; and

[0109] the base station assigns traffic channels to the paged mobiles onwhich to receive their pending packets and broadcasts their identity onthe downlink notification sub-frame.

[0110] III. Performance of the Medium Access Control Scheme

[0111] The performance of the proposed interference-sensing scheme fordownlink and uplink channel assignment is measured in terms of the dropin the S/I ratio or the increase in the retransmission probability theproposed scheme would help prevent when compared to a scheme thatemploys mobile measurements only. A system of sectorized cells isconsidered, each having three sectors with a 120-degree beam-width witha front-to-back ratio of 20 dB.

[0112] Two layouts are considered. One is a hexagonal pattern, asillustrated in FIG. 12. sector D1 might re-use the channels used bysectors B1 and E1 since the mobile performing interference measurementswould not receive a sufficiently strong signal from these sectors.Conversely, a mobile in sector E1 could receive co-channel interferencecontributed by sectors A1 D1, I1, and L1. Moreover, if the mobilesactive in the coverage area of sectors B1 and J1 are shielded from thesignal from sector E1, sectors B1 and J1 could also contribute to theinterference at mobile m. Assuming an interference limited system, apropagation loss coefficient of 4, and a measured S/I ratio of 10 dB,the S/I ratio penalty experienced by a mobile at location m in thecoverage area of sector E1 could be as high as 4.25 dB, as shown inAppendix I.

[0113] Also a system arranged in a cloverleaf pattern is considered, asillustrated in FIG. 13. In this situation sector H1 might re-use thechannels used by sectors D1, E1, and I1 since the mobile performinginterference measurements would not receive a sufficiently strong signalfrom these sectors. Conversely, a mobile in sector E1 could receiveco-channel interference contributed by sectors D1, I1, and H1. The S/Iratio penalty experienced by a mobile at location m in the coverage areaof sector E1 could be as high as 3.99 dB for this arrangement, as shownin Appendix I.

[0114] An S/I ratio penalty of such magnitude would cause aword-error-rate experienced in packet transmission, and packetre-transmission probability, higher by an order of magnitude for theOFDM signal analyzed in the L. J. Cimini, Jr., et al. reference citedabove, when employing four transmit and two receive antennas for 40-μsecdelay spread, 10-Hz Doppler, and QPSK with differential detection and½-rate Reed-Solomon coding.

[0115] One might be tempted to dismiss this result because location m isjust one location and the impact on the average S/I ratio [or otherstatistical metric] might be less severe. To this one would rebut thatthe interference penalty realized at other locations may be either loweror higher depending on the power control policy employed and the rulesfor channel assignment, typically prescribed by the dynamic channelassignment algorithm implemented in conjunction with interferencesensing. For instance, consider the case where both Sectors D1 and I1assigned the same channel as that assigned to a mobile served by SectorE1 to transmit packets to mobiles located on their respective cellboundaries; namely locations n and l, respectively. If the power controlpolicy equalized the received signal strength, most mobile locations inSector El could experience a lower S/I ratio than location m as they arecloser to base stations D and I. Different scenarios could be describedwhereby location m would experience the lowest S/I ratio of alllocations in Sector E1.

[0116] But even if all other locations in Sector E1 experienced a higherS/I ratio than location m, and as a result the S/I statistics across thecell are affected less severely by an interference-sensing scheme thatmisses some times, that would not be relevant to users of fixed wirelesssystems, for instance. They stay in the same position, alwaysexperiencing the same performance. Unlike with mobile users, whosemovement to different locations will result in a better averageperformance, the higher S/I ratio experienced elsewhere in the cell isirrelevant to the fixed-wireless user. The same applies to portablecomputing users if they are likely to select their point of connectionbased on factors other than signal quality.

[0117] Of course, it is possible to design heuristic channel assignmentalgorithms that compensate for the missing interference information. Forexample, measurement-based dynamic channel assignment combined withchannel segregation, See F. Furuya and Y. Akaiwa, “Channel segregation,a distributed adaptive channel allocation scheme for mobilecommunications systems”, Trans. IEICE, Vol. E74, June 1991, pp.1531-1537. There, re-use patterns are determined from empiricallyobserved transmission successes and failures, helps avoid situationslike those described in this section. See the L. J. Cimini, Jr., et al.reference cited above. Greater efficiency would be achieved, however, ifco-channel interference was avoided reliably (through the use of theproposed interference-sensing scheme) and the channel assignmentalgorithm was selected to better focus on maximizing throughput.

[0118] The performance of the interference-sensing scheme of the presentinvention may be quantified in terms of the deterioration of the qualityof service requirement it helps prevent. For example, in the case inwhich the CAA criterion employed for downlink channel assignment reliesonly upon mobile measurements, the result would be substantialinterference increase. An example of base stations arranged in ahexagonal pattern is shown in FIG. 14. FIG. 14 shows a plurality of basestations 1101-1112, each base station having three sectors with a120-degree beamwidth. For example, base station 1101 has three sectors1101-1, 1101-2, and 1101-3. If the front-to-back ratio is 20 dB, sector1104-1 could re-use the channels used by sectors 1102-1 and 1105-1 sincethe mobile stations performing interference measurements would notreceive a sufficiently strong signal from these sectors. Conversely, amobile in sector 1105-1 could receive co-channel interferencecontributed by sectors 1101-1, 1104-1, and 1109-1.

[0119] Assuming an interference limited system, a propagation losscoefficient of 4, and a target S/I ratio of 10 dB, the S/I ratio penaltyexperienced by a mobile station in the coverage area of sector 1105-1could be as high as 3 dB. A penalty of such magnitude would cause theword-error-rate experienced in packet transmission, and the packetre-transmission probability, to increase by an order of magnitude whenemploying four transmit and two receive antennas for 40-μsec delayspread, 10-Hz Doppler, and QPSK with differential detection and ½ rateReed-Solomon coding.

[0120] A. Other Considerations

[0121] 1. Battery-life Awareness

[0122] This protocol imposes little additional burden of the battery ofthe mobiles. Although mobiles are asked to broadcast their assignedtones, this is required only of the paged mobiles that have beenassigned a channel and are ready to receive/transmit in a super-frame.The broadcast occurs only during the assignment portion of thatsuper-frame.

[0123] It is important to note that while the present invention has beendescribed in the context of a fully functioning data processing system,those of ordinary skill in the art will appreciate that the processes ofthe present invention are capable of being distributed in the form of acomputer readable medium of instructions and a variety of forms and thatthe present invention applies equally regardless of the particular typeof signal bearing media actually used to carry out the distribution.Examples of computer readable media include recordable-type media suchas floppy disc, a hard disk drive, RAM, and CD-ROM's, as well astransmission-type media, such as digital and analog communicationslinks.

[0124] The resulting invention provides an interference-sensing mediumaccess method that meets this condition for asymmetric dynamic channelassignment. The invention can be used with traffic consisting of eithercircuit-switched calls or with packets; the packet length may eitherfixed or variable.

[0125] It is to be understood that the above-described embodiments aremerely illustrative of the principles of the invention. Variousmodifications and changes may be made thereto by those skilled in theart that will embody the principles of the invention and fall within thespirit and scope thereof.

What is claimed is:
 1. A method of assigning a downlink channel to amobile station registered with a base station, comprising the steps of:a) turning off pilot tones being transmitted by a plurality of activemobile stations registered with the base station, each turned off pilottone corresponding to an assigned downlink channel; b) paging the mobilestation with a pending traffic packet from the base station; c)performing interference sensing at the base station to identifyinterference-free downlink channels; d) assigning, at the base station,a downlink traffic channel to the mobile station to receive the pendingpackets; and e) transmitting the downlink channel assignment from thebase station to the mobile station.
 2. The method of claim 1 , whereindownlink channels are assigned to a plurality of mobile stationsregistered with the base station.
 3. The method of claim 1 , whereinthere are a plurality of base stations and steps a)-e) are performedsuccessively for each of the plurality of base stations.
 4. A method ofassigning an uplink channel to a mobile station registered with a basestation, comprising the steps of: a) turning off pilot tones beingtransmitted by the base station, each pilot tones corresponding to anuplink channel assigned to one of a plurality of active mobile stationsregistered with the base station; b) requesting access from the mobilestation for a traffic packet; c) performing interference sensing at theplurality of active mobile stations to identify interference-free uplinkchannels; d) transmitting from each one of the plurality of activemobile stations a list of uplink channels identified as being acceptablyinterference-free; e) assigning, at the base station, an uplink channelto the mobile station; and f) transmitting the uplink channel assignmentfrom the base station to the mobile station.
 5. The method of claim 4 ,wherein uplink channels are assigned to a plurality of mobile stationsregistered with the base station.
 6. The method of claim 4 , whereinthere are a plurality of base stations and steps a)-f) are performedsuccessively for each of the plurality of base stations.
 7. A method ofassigning an uplink channel and a downlink channel to a mobile stationregistered with a base station, comprising the steps of: a) turning offpilot tones being transmitted by a plurality of active mobile stationsregistered with the base station, each turned off pilot tonecorresponding to an assigned downlink channel; b) turning off pilottones being transmitted by the base station, each pilot tonescorresponding to an uplink channel assigned to one of the plurality ofactive mobile stations registered with the base station; c) paging themobile station with a pending traffic packet from the base station; d)requesting access from the mobile station for a traffic packet; e)performing interference sensing at the base station to identifyinterference-free downlink channels; f) performing interference sensingat the plurality of active mobile stations to identify interference-freeuplink channels; g) transmitting from each one of the plurality ofactive mobile stations a list of uplink channels identified as beingacceptably interference-free; h) assigning, at the base station, adownlink traffic channel to the mobile station to receive the pendingpackets; i) assigning, at the base station, an uplink channel to themobile station; and j) transmitting the downlink channel assignment andthe uplink channel assignment from the base station to the mobilestation.
 8. The method of claim 7 , wherein downlink channels and uplinkchannels are assigned to a plurality of mobile stations registered withthe base station.
 9. The method of claim 7 , wherein there are aplurality of base stations and steps a)-j) are performed successivelyfor each of the plurality of base stations.
 10. A system for assigning adownlink channel to a mobile station registered with a base station,comprising: means for turning off pilot tones being transmitted by aplurality of active mobile stations registered with the base station,each turned off pilot tone corresponding to an assigned downlinkchannel; means for paging the mobile station with a pending trafficpacket from the base station; means for performing interference sensingat the base station to identify interference-free downlink channels;means for assigning, at the base station, a downlink traffic channel tothe mobile station to receive the pending packets; and means fortransmitting the downlink channel assignment from the base station tothe mobile station.
 11. The system of claim 10 , wherein downlinkchannels are assigned to a plurality of mobile stations registered withthe base station.
 12. The system of claim 10 , wherein there are aplurality of base stations and the system operates on each of theplurality of base stations.
 13. A system for assigning an uplink channelto a mobile station registered with a base station, comprising: meansfor turning off pilot tones being transmitted by the base station, eachpilot tones corresponding to an uplink channel assigned to one of aplurality of active mobile stations registered with the base station;means for requesting access from the mobile station for a trafficpacket; means for performing interference sensing at the plurality ofactive mobile stations to identify interference-free uplink channels;means for transmitting from each one of the plurality of active mobilestations a list of uplink channels identified as being acceptablyinterference-free; means for assigning, at the base station, an uplinkchannel to the mobile station; and means for transmitting the uplinkchannel assignment from the base station to the mobile station.
 14. Thesystem of claim 13 , wherein downlink channels are assigned to aplurality of mobile stations registered with the base station.
 15. Thesystem of claim 13 , wherein there are a plurality of base stations andthe system operates on each of the plurality of base stations.
 16. Asystem for assigning an uplink channel and a downlink channel to amobile station registered with a base station, comprising: means forturning off pilot tones being transmitted by a plurality of activemobile stations registered with the base station, each turned off pilottone corresponding to an assigned downlink channel; means for turningoff pilot tones being transmitted by the base station, each pilot tonescorresponding to an uplink channel assigned to one of the plurality ofactive mobile stations registered with the base station; means forpaging the mobile station with a pending traffic packet from the basestation; means for requesting access from the mobile station for atraffic packet; means for performing interference sensing at the basestation to identify interference-free downlink channels; means forperforming interference sensing at the plurality of active mobilestations to identify interference-free uplink channels; means fortransmitting from each one of the plurality of active mobile stations alist of uplink channels identified as being acceptablyinterference-free; means for assigning, at the base station, a downlinktraffic channel to the mobile station to receive the pending packets;means for assigning, at the base station, an uplink channel to themobile station; and means for transmitting the downlink channelassignment and the uplink channel assignment from the base station tothe mobile station.
 17. The system of claim 16 , wherein downlinkchannels and uplink channels are assigned to a plurality of mobilestations registered with the base station.
 18. The system of claim 16 ,wherein there are a plurality of base stations and the system operateson each of the plurality of base stations.
 19. A computer programproduct for assigning a downlink channel to a mobile station registeredwith a base station, comprising: a computer readable medium; computerprogram instructions, recorded on the computer readable medium,executable by a processor, for performing the steps of: a) turning offpilot tones being transmitted by a plurality of active mobile stationsregistered with the base station, each turned off pilot tonecorresponding to an assigned downlink channel; b) paging the mobilestation with a pending traffic packet from the base station; c)performing interference sensing at the base station to identifyinterference-free downlink channels; d) assigning, at the base station,a downlink traffic channel to the mobile station to receive the pendingpackets; and e) transmitting the downlink channel assignment from thebase station to the mobile station.
 20. The computer program product ofclaim 19 , wherein downlink channels are assigned to a plurality ofmobile stations registered with the base station.
 21. The computerprogram product of claim 19 , wherein there are a plurality of basestations and steps a)-e) are performed successively for each of theplurality of base stations.
 22. A computer program product for assigninga uplink channel to a mobile station registered with a base station,comprising: a computer readable medium; computer program instructions,recorded on the computer readable medium, executable by a processor, forperforming the steps of: a) turning off pilot tones being transmitted bythe base station, each pilot tones corresponding to an uplink channelassigned to one of a plurality of active mobile stations registered withthe base station; b) requesting access from the mobile station for atraffic packet; c) performing interference sensing at the plurality ofactive mobile stations to identify interference-free uplink channels; d)transmitting from each one of the plurality of active mobile stations alist of uplink channels identified as being acceptablyinterference-free; e) assigning, at the base station, an uplink channelto the mobile station; and f) transmitting the uplink channel assignmentfrom the base station to the mobile station.
 23. The computer programproduct of claim 22 , wherein downlink channels are assigned to aplurality of mobile stations registered with the base station.
 24. Thecomputer program product of claim 22 , wherein there are a plurality ofbase stations and steps a)-f) are performed successively for each of theplurality of base stations.
 25. A computer program product for assigningan uplink channel and a downlink channel to a mobile station registeredwith a base station, comprising: a computer readable medium; computerprogram instructions, recorded on the computer readable medium,executable by a processor, for performing the steps of: a) turning offpilot tones being transmitted by a plurality of active mobile stationsregistered with the base station, each turned off pilot tonecorresponding to an assigned downlink channel; b) turning off pilottones being transmitted by the base station, each pilot tonescorresponding to an uplink channel assigned to one of the plurality ofactive mobile stations registered with the base station; c) paging themobile station with a pending traffic packet from the base station; d)requesting access from the mobile station for a traffic packet; e)performing interference sensing at the base station to identifyinterference-free downlink channels; f) performing interference sensingat the plurality of active mobile stations to identify interference-freeuplink channels; g) transmitting from each one of the plurality ofactive mobile stations a list of uplink channels identified as beingacceptably interference-free; h) assigning, at the base station, adownlink traffic channel to the mobile station to receive the pendingpackets; i) assigning, at the base station, an uplink channel to themobile station; and j) transmitting the downlink channel assignment andthe uplink channel assignment from the base station to the mobilestation.
 26. The computer program product of claim 25 , wherein downlinkchannels and uplink channels are assigned to a plurality of mobilestations registered with the base station.
 27. The computer programproduct of claim 25 , wherein there are a plurality of base stations andsteps a)-j) are performed successively for each of the plurality of basestations.
 28. A method for medium access control for uncoupled downlinkand uplink channel assignment, comprising: assigning a base station aframe within a periodic super-frame during which it transmits;transmitting narrow-band pilot tones from the base station,corresponding to assigned traffic channels between base station andtheir mobiles; scanning the tones from the base station by mobiles andreporting a list of channels with low interference back to the basestation; said scanning being in a staggered order to avoid contentionfor a same channel between mutually interfering base stations withconcurrent traffic; and selecting at the base station a channel andnotifying the mobile.
 29. A system for medium access control foruncoupled downlink and uplink channel assignment, comprising: a basestation having an assigned frame within a periodic super-frame duringwhich it transmits; said base station transmitting narrow-band pilottones, corresponding to assigned traffic channels between the basestation and mobile stations; a mobile station scanning the tones fromthe base station by mobiles and reporting a list of channels with lowinterference back to the base station; said scanning being in astaggered order to avoid contention for a same channel between mutuallyinterfering base stations with concurrent traffic; and said base stationselecting a channel and notifying the mobile.